WEDNESDAY, March 20 (HealthDay News) -- Rates of premature death in counties across the United States are the lowest in 20 years, but people in the least healthy counties are more than twice as likely to die early as those in the healthiest counties, according to a new report.

In addition, childhood poverty rates in unhealthy counties are twice as high as those in healthy counties, according to the 2013 County Health Rankings released by the Robert Wood Johnson Foundation and the University of Wisconsin Population Health Institute.

This is the fourth year of the rankings, which examine 25 factors that influence health, including rates of smoking, obesity levels, teen birth rates, access to doctors and dentists, child poverty, physical activity levels, high school graduation rates and percentages of children living in single-parent homes.

The rankings also take into account how long people live and how well they feel.

This year's rankings identified significant new national trends:

Child poverty rates have not improved since 2000, and more than one in five children currently lives in poverty.

Violent crime has decreased by almost 50 percent over the past two decades.

Counties where people don't live as long and have poorer physical and mental health have the highest rates of smoking, teen births, physical inactivity and preventable hospital stays.

Teen birth rates are more than twice as high in the least healthy counties as in the healthiest counties.

People in healthier counties are 1.4 times more likely to have access to a doctor and dentist than those in the least healthy counties.

The rankings "can be put to use right away by leaders in government, business, health care and every citizen motivated to work together to create a culture of health in their community," Dr. Risa Lavizzo-Mourey, president and CEO of the Robert Wood Johnson Foundation, said in a County Health Rankings news release. "The rankings are driving innovation, unleashing creativity and inspiring big changes to improve health in communities large and small throughout the country."

Dr. Patrick Remington, professor and associate dean at the University of Wisconsin School of Medicine and Public Health, said no single sector alone can tackle the health challenges in any given community.

"Collaboration is critical," he said in the news release. "The rankings are sparking action all over the country as people from all sectors join forces to create new possibilities in health -- county by county."